An example of such a device is a valve regulator in which the valve control is carried out by a rotatable control member in the shape of a cog wheel or a cog sector, which is operated by a linearly moveable member in the shape of a toothed rack, which can be connected to or be part of a nut which co-operates with a rotatable screw, the rotation of the screw controlling the operation of the valve. The screw may, for example, be driven by an electric monitor which is controlled in any suitable way.
In motion transmitting mechanisms working intermittently, e.g., valve regulators, there is frequently a considerable difference between the force required to start motion and the force required to maintain the motion. This is due to the fact that the coefficient of static friction is, generally, higher than the coefficient of sliding friction and that an apparatus is generally difficult to start after a time of immobility. Specifically, it may be difficult to open or close valves which have been completely closed or open for a while. A conventional driving mechanism for this purpose must, therefore, be dimensioned for a great force, which is developed only a short time during each motion occasion.